This invention relates to pigment preparations, a process for their preparation, a process for pigmenting organic macromolecular material, especially plastics based on polyurethane, and the use of pigment preparations comprising polyisocyanate addition products for pigmenting polyurethane foams.
Polyurethanes that can be used as paint binders or coating material, for example, for textiles, are produced in a wide range in the form of one- or two-component systems, in a highly flexible or rigid form, with or without a solvent content. If such materials are pigmented, it is a problem finding a suitable pigment vehicle in which the pigments can be dispersed in high concentration without flocculation and which is compatible with the various polyurethanes so that a specific pigment paste need not be tailored for each specific system. For the two-component systems that are customary in the paint industry, the only available pigmenting vehicle is usually the relatively low viscosity polyol component, in which not only carbon black or organic pigments such as phthalocyanines but also inorganic pigments such as iron oxide yellow or iron oxide red cannot be dispersed without flocculation and thixotropy. Not only does this make every grind problematical and uneconomical, but it also continues to have an adverse effect on flow, gloss, depth of shade, hiding power, and gloss durability of the cured paint films even after the isocyanate component has been added.
Polyurethane coating materials for textiles comprise very high molecular weight species which have only limited miscibility with one another (one- or two-component systems) and their viscosity alone makes it impossible to achieve high pigment concentrations.
In addition to these homogeneous polyurethanes, cellular polyurethanes, which can vary in their elasticity from rigid to extremely flexible foams, have attained great importance. These foams are mainly colored shortly before foaming in a mixing head in which polyols and polyisocyanates are intimately mixed with color pastes in the absence or presence of auxiliaries. The binders in these color pastes are usually polyester or polyether polyols which, however, have a pigment-holding capacity so low, especially with respect to carbon black, that the color pastes have high viscosities at carbon black concentrations as low as 10 to 18%. A normal addition of a color paste in a proportion of 3 to 5% by weight, based on the sum of all the ingredients of the foam, which is too low to affect the mechanical characteristics of the foam to any great extent, does not produce a deep color but, for example, in the case of carbon black, gives only a grey coloration.
To achieve deep colors in the material to be pigmented, to ensure meterability in the production of the material, and to minimize the effect of the binder on the mechanical characteristics of these materials, especially foams, it would be desirable to obtain readily pumpable pastes having high pigment contents.
A combination of good color-paste pumpability and flowability, coupled with the desired high pigment contents, also plays an important role in the production of the color pastes. Highly viscous and/or nonflowable pastes can be industrially produced only on roll mills or in kneaders; production using continuous stirred bead mills is not possible.
It is an object of the present invention to provide pigment preparations which have a very low viscosity and also good flow properties throughout the entire production process, especially in continuously stirred bead mills, and thus are particularly economical to produce.
The literature discloses several attempts to achieve these goals. German Offenlegungsschrift 3,115,651 discloses adding a polyvinylpyrrolidone to the polyether polyol binder as a viscosity-reducing additive German Offenlegungsschrift 3,803,810 discloses a copolymer of .alpha.-olefin and .alpha.,.beta.-unsaturated dicarboxylic esters as binder additive. Further known additives for polyester polyol or polyether polyol binders include organotitanium compounds (German Offenlegungsschrift 4,236,709) and oil-modified polyurethanes (European Patent Application 603,546). German Offenlegungsschrift 2,402,839, by contrast, uses a carbodiimide-functional resin as pigment vehicle.
The prior art pigment preparations, however, have some disadvantages. For example, some additives or binder systems usually work only with certain pigments. Furthermore, the pigment tends to agglomerate in the known preparations, so that the desired color strength cannot be achieved in the material to be colored. With some of these preparations, undesirable agglomeration or aggregate formation occurs as a consequence of the dilution effect of the paste, for example, during the foaming process of polyurethane, the result of which is again that the desired color depth is not achieved. In addition, it is necessary to increase the color strength of the polyurethane foam to be pigmented while at the same time improving the viscosity and flow behavior of the preparation.
It has now been found that such disadvantages can be overcome with the pigment pastes of the invention.